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Thursday, May 5, 2011

When aphids attack

Sorry if the title of this post sounds like a cheap special on the Fox Network. I couldn’t help myself. But the truth is that our peaceable town is under siege. Not by hungry gila monsters or blood-thirsty vampire bats, but by aphids. Just yesterday I was waiting at a stoplight near the post office, and I happened to glance at the roses planted in the median strip. The buds and stems were covered so densely that they looked like they were bulging like grotesque neoplasms, and the leaves were so shiny from all the aphid excretions that you could have gotten the impression that it had just rained.

As much as I like roses, we took out all the bushes we inherited when we bought our house in 1997 for two reasons: They were aphid magnets in the spring and hence a nasty mess for a good number of months, and the spines are not exactly child-friendly.

Fast forward 14 years and our garden is relatively aphid-free except for some bamboos that aren’t so lucky. I have no idea why some bamboo species attract aphids like catnip attracts cats, and other don’t. You’d think bamboo leaves would all “taste” the same?!?

Semiarundinaria fastuosa with aphids

These bamboo species in our garden seem to be particularly prone to aphid attacks:

Quite a few lady bugs hanging out on the infested plants. According to the web site Ladybug Lady, an adult lady bug eats about 50 aphids a day. That sounds pretty good until you realize that under optimal conditions, a single aphid could produce 600 billion offspring in one season.

As the thermometer climbs into the 90s, the aphids will eventually go away (where? Oregon?), but for now I spray the affected plants with insecticidal soap. For it to be successful, the application has to be repeated every 3 or 4 days. It gets tedious after a while and isn’t easy to do on a plant that is 6 ft. tall. Since I still have the use of our neighbor’s pressure washer that I used the other week to clean our flagstone walkway and patio, I’m planning on giving all our taller aphid-infested bamboos a good hosing down on the lowest setting. Maybe that is enough to reduce the aphid population to a tolerable level.

Much like aphids appear to have a preference for certain bamboo species over others, the same holds true for succulents. Our coral aloes (Aloe striata), currently in flower, are infested while other blooming aloes aren’t. Some echeveria and graptopetalum flowers seem to be aphid magnets whereas other succulents flowers are completely aphid-free. If there’s a pattern, I can’t see it.

Here are photos of two of our coral aloes (Aloe striata) that are currently in flower. One is infested with black aphids, the other white. Supposedly the color of aphids is determined by the food they eat, but both sets of flowers are salmon-colored. Go figure!

Coral aloe (Aloe striata) flower with black aphids

Coral aloe (Aloe striata) flower with white aphids

According to Wikipedia, there are 4,400 species of aphids in 10 families. Many of which infest only one plant species while others feed on hundreds of different plant species. I harbor no illusions that I will ever achieve a lasting victory over the little buggers.

Strong spray of water should take care of a lot of them -- once they're knocked off the plant they have no way of getting back up. They're not big on walking too much.

I don't mind a few aphids, but an army of them is nasty. Their sticky droppings are the worst part, but I've also heard that they're "good" at spreading disease. Which is weird, because how exactly do they move between plants if they don't move much? Hmmm... conflicting information.

Aphids are a proper pain in the garden. A large British Sycamore (Acer pseudoplatanus)down the bottom of our garden is reliably infested with it every year, dropping sticky sap all over the area.

Alan, they are largely implicated for the spread of the Canna virus as they suck from one plant to another.

Gerhard, some species of bamboo are notorious for being aphid magnets for some unknown reason, P. bambusoides and its cultivars is one of them. I remember an anecdote wherein a group of bamboo experts here were baffled were trying to ID an unidentified bamboo, and came to a conclusion it is Bambusoides on the basis that it was covered in aphids :)

Alan, in addition to white and black aphids we also have winged green aphids. They fly and definitely get around!!

Mark and Gaz, I loved that anecdote!! I don't think I've ever seen aphids on a Fargesia or Bambusa (knock on wood). Right now, Semiarundinaria fastuosa is the hardest hit. In fact, I just sprayed it with water in hopes of knocking a large part of the aphids off.